Polarised light micrograph of aplite from the former Schrofel quarry, Heselbach, Black Forest, Germany. Aplite is an intrusive igneous rock with the same mineral composition as granite, but with much finer grains (less than 1 millimetre diameter). The fine nature is due to rapid crystallisation of the rock's components. Quartz and alkali feldspar (usually orthoclase or microperthite) are the dominant minerals with microcline and albite also present. Magnification: x30 when printed at 15 centimetres wide.